Planetary gear train of automatic transmission for vehicle

ABSTRACT

A planetary gear train of an automatic transmission for a vehicle may include an input shaft to receive torque of an engine, an output shaft to output changed torque of the engine, a first planetary gear set including first, second, and third rotation elements, a second planetary gear set including fourth, fifth, and sixth rotation elements, a third planetary gear set including seventh, eighth, and ninth rotation elements, and a fourth planetary gear set including tenth, eleventh, and twelfth rotation elements.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to Korean Patent Application No.10-2015-0170987, filed Dec. 2, 2015, the entire contents of which isincorporated herein for all purposes by this reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an automatic transmission for avehicle. More particularly, the present invention relates to a planetarygear train of an automatic transmission for a vehicle that improvespower delivery performance and fuel economy by achieving at least nineforward speed stages and widening speed ratio (or gear ratio) with aminimum number of constituent elements being used, and secures linearityof step ratios.

Description of Related Art

Recent increases in oil prices are triggering hard competition amongauto-makers in enhancing fuel consumption of a vehicle.

In this sense, research is being conducted on engines in terms ofreducing weight and improving fuel efficiency by down-sizing, andresearch is also being conducted to ensure both drivability andcompetitiveness for maximizing fuel efficiency by implementing anautomatic transmission with multiple speed stages.

However, in the case of the automatic transmission, the number ofinternal components increases as the number of gear shift stages isincreased, which may deteriorate installability, production cost, weightand/or power flow efficiency.

Therefore, in order to maximally enhance fuel consumption of anautomatic transmission having more shift-stages, it is important thatbetter efficiency is achieved using a smaller number of parts.

In this aspect, in recent years, 8-speed automatic transmissions tend tobe implemented and the research and development of a planetary geartrain capable of implementing more speed stages has also been activelyconducted.

However, since a conventional 8-speed automatic transmission has gearratio span of 6.5-7.5, improvement of power performance and fuel economymay not be great.

In addition, if 8-speed automatic transmission has gear ratio spanlarger than 9.0, it is hard to secure linearity of step ratios.Therefore, driving efficiency of an engine and drivability of a vehiclemay be deteriorated, and thus, development of high efficiency automatictransmissions which achieve at least nine forward speed stages isnecessary.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention andtherefore it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

BRIEF SUMMARY

Various aspects of the present invention are directed to providing aplanetary gear train of an automatic transmission for a vehicle havingadvantages of improving power delivery performance and fuel economy byachieving nine forward speed stages and one reverse speed stage, andwidening gear ratio span and of securing linearity of step ratios.

According to various aspects of the present invention, a planetary geartrain of an automatic transmission for a vehicle may include an inputshaft to receive torque of an engine, an output shaft to output changedtorque of the engine, a first planetary gear set including first,second, and third rotation elements, a second planetary gear setincluding fourth, fifth, and sixth rotation elements, a third planetarygear set including seventh, eighth, and ninth rotation elements, and afourth planetary gear set including tenth, eleventh, and twelfthrotation elements, in which the input shaft may be directly connected tothe first rotation element, the output shaft may be directly connectedto the twelfth rotation element, the second rotation element may bedirectly connected to the sixth rotation element and the ninth rotationelement, the fifth rotation element may be directly connected to theeleventh rotation element, the eighth rotation element may be directlyconnected to the tenth rotation element, and the second rotation elementmay be selectively connected to a transmission housing.

The third rotation element may be selectively connected to thetransmission housing, the fourth rotation element may be selectivelyconnected to the transmission housing, the input shaft may beselectively connected to the eleventh rotation element, the input shaftmay be selectively connected to the seventh rotation element, and thethird rotation element may be selectively connected to the seventhrotation element.

The first, second, and third rotation elements may be a first sun gear,a first ring gear, and a first planet carrier, the fourth, fifth, andsixth rotation elements may be a second sun gear, a second planetcarrier, and a second ring gear, the seventh, eighth, and ninth rotationelements may be a third sun gear, a third planet carrier, and a thirdring gear, and the tenth, eleventh, and twelfth rotation elements may bea fourth sun gear, a fourth planet carrier, and a fourth ring gear.

The planetary gear train may further include a first clutch selectivelyconnecting the input shaft to the eleventh rotation element, a secondclutch selectively connecting the input shaft to the seventh rotationelement, a third clutch selectively connecting the third rotationelement to the seventh rotation element, a first brake selectivelyconnecting the second rotation element to the transmission housing, asecond brake selectively connecting the third rotation element to thetransmission housing, and a third brake selectively connecting thefourth rotation element to the transmission housing.

According to various aspects of the present invention, a planetary geartrain of an automatic transmission for a vehicle may include an inputshaft receiving torque of an engine, an output shaft outputting changedtorque of the engine, a first planetary gear set including first,second, and third rotation elements, a second planetary gear setincluding fourth, fifth, and sixth rotation elements, a third planetarygear set including seventh, eighth, and ninth rotation elements, afourth planetary gear set including tenth, eleventh, and twelfthrotation elements, a first rotation shaft directly connected to thefirst rotation element and directly connected to the input shaft, asecond rotation shaft directly connecting the second rotation element tothe sixth rotation element and the ninth rotation element, andselectively connected to a transmission housing, a third rotation shaftdirectly connected to the third rotation element and selectivelyconnected to the transmission housing, a fourth rotation shaft directlyconnected to the fourth rotation element and selectively connected tothe transmission housing, a fifth rotation shaft directly connecting thefifth rotation element to the eleventh rotation element and selectivelyconnected to the input shaft, a sixth rotation shaft directly connectedto the seventh rotation element and selectively connected to the inputshaft or the third rotation shaft, a seventh rotation shaft directlyconnecting the eighth rotation element to the tenth rotation element,and an eighth rotation shaft directly connected to the twelfth rotationelement and directly connected to the output shaft.

The first planetary gear set may be a double pinion planetary gear set,the first rotation element may be a first sun gear, the second rotationelement may be a first ring gear, and the third rotation element may bea first planet carrier, the second planetary gear set may be a singlepinion planetary gear set, the fourth rotation element may be a secondsun gear, the fifth rotation element may be a second planet carrier, andthe sixth rotation element may be a second ring gear, the thirdplanetary gear set may be a single pinion planetary gear set, theseventh rotation element may be a third sun gear, the eighth rotationelement may be a third planet carrier, and the ninth rotation elementmay be a third ring gear, and the fourth planetary gear set may be asingle pinion planetary gear set, the tenth rotation element may be afourth sun gear, the eleventh rotation element may be a fourth planetcarrier, and the twelfth rotation element may be a fourth ring gear.

The planetary gear train may further include a first clutch selectivelyconnecting the input shaft to the fifth rotation shaft, a second clutchselectively connecting the input shaft to the sixth rotation shaft, athird clutch selectively connecting the third rotation shaft to thesixth rotation shaft, a first brake selectively connecting the secondrotation shaft to the transmission housing, a second brake selectivelyconnecting the third rotation shaft to the transmission housing, and athird brake selectively connecting the fourth rotation shaft to thetransmission housing.

A first forward speed stage may be achieved by operation of the thirdclutch and the first and third brakes, a second forward speed stage maybe achieved by operation of the third clutch and the second and thirdbrakes, a third forward speed stage may be achieved by operation of thesecond and third clutches and the third brake, a fourth forward speedstage may be achieved by operation of the first and third clutches andthe third brake, a fifth forward speed stage may be achieved byoperation of the first and second clutches and the third brake, a sixthforward speed stage may be achieved by operation of the first, second,and third clutches, a seventh forward speed stage may be achieved byoperation of the first and second clutches and the second brake, aneighth forward speed stage may be achieved by operation of the first andthird clutches and the second brake, a ninth forward speed stage may beachieved by operation of the first and third clutches and the firstbrake, and a reverse speed stage may be achieved by operation of thesecond clutch and the first and third brakes.

According to various aspects of the present invention, a planetary geartrain of an automatic transmission for a vehicle may include an inputshaft receiving torque of an engine, an output shaft outputting changedtorque of the engine, a first planetary gear set which may be a doublepinion planetary gear set including first, second, and third rotationelements, a second planetary gear set which may be a single pinionplanetary gear set including fourth, fifth, and sixth rotation elements,a third planetary gear set which may be a single pinion planetary gearset including seventh, eighth, and ninth rotation elements, a fourthplanetary gear set which may be a single pinion planetary gear setincluding tenth, eleventh, and twelfth rotation elements, a firstrotation shaft directly connected to the first rotation element anddirectly connected to the input shaft, a second rotation shaft directlyconnecting the second rotation element to the sixth rotation element andthe ninth rotation element, and selectively connected to a transmissionhousing, a third rotation shaft directly connected to the third rotationelement and selectively connected to the transmission housing, a fourthrotation shaft directly connected to the fourth rotation element andselectively connected to the transmission housing, a fifth rotationshaft directly connecting the fifth rotation element to the eleventhrotation element and selectively connected to the input shaft, a sixthrotation shaft directly connected to the seventh rotation element andselectively connected to the input shaft or the third rotation shaft, aseventh rotation shaft directly connecting the eighth rotation elementto the tenth rotation element, an eighth rotation shaft directlyconnected to the twelfth rotation element and directly connected to theoutput shaft, a first clutch selectively connecting the input shaft tothe fifth rotation shaft, a second clutch selectively connecting theinput shaft to the sixth rotation shaft, a third clutch selectivelyconnecting the third rotation shaft to the sixth rotation shaft, a firstbrake selectively connecting the second rotation shaft to thetransmission housing, a second brake selectively connecting the thirdrotation shaft to the transmission housing, and a third brakeselectively connecting the fourth rotation shaft to the transmissionhousing.

Various embodiment of the present invention achieve at least nineforward speed stages and one reverse speed stage by combining fourplanetary gear sets, which are simple planetary gear sets, with sixcontrol elements.

In addition, since gear ratio span greater than 9.0 is secured, drivingefficiency of the engine may be maximized.

Furthermore, since linearity of step ratios can be secured due tomultiple speed stages, drivability such as acceleration before and aftershift, rhythmical engine speed, and on the like may be improved.

It is understood that the term “vehicle” or “vehicular” or other similarterms as used herein is inclusive of motor vehicles in general such aspassenger automobiles including sports utility vehicles (SUV), buses,trucks, various commercial vehicles, watercraft including a variety ofboats and ships, aircraft, and the like, and includes hybrid vehicles,electric vehicles, plug-in hybrid electric vehicles, hydrogen-poweredvehicles and other alternative fuel vehicles (e.g., fuel derived fromresources other than petroleum). As referred to herein, a hybrid vehicleis a vehicle that has two or more sources of power, for example, bothgasoline-powered and electric-powered vehicles.

The methods and apparatuses of the present invention have other featuresand advantages which will be apparent from or are set forth in moredetail in the accompanying drawings, which are incorporated herein, andthe following Detailed Description, which together serve to explaincertain principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a planetary gear train according tovarious embodiments of the present invention.

FIG. 2 is an operation chart of control elements at each speed stage inthe planetary gear train according to various embodiments of the presentinvention.

It should be understood that the appended drawings are not necessarilyto scale, presenting a somewhat simplified representation of variousfeatures illustrative of the basic principles of the invention. Thespecific design features of the present invention as disclosed herein,including, for example, specific dimensions, orientations, locations,and shapes will be determined in part by the particular intendedapplication and use environment.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments of thepresent invention(s), examples of which are illustrated in theaccompanying drawings and described below. While the invention(s) willbe described in conjunction with exemplary embodiments, it will beunderstood that the present description is not intended to limit theinvention(s) to those exemplary embodiments. On the contrary, theinvention(s) is/are intended to cover not only the exemplaryembodiments, but also various alternatives, modifications, equivalentsand other embodiments, which may be included within the spirit and scopeof the invention as defined by the appended claims.

FIG. 1 is a schematic diagram of a planetary gear train according tovarious embodiments of the present invention.

Referring to FIG. 1, a planetary gear train according to variousembodiments of the present invention includes first, second, third, andfourth planetary gear sets PG1, PG2, PG3, and PG4 disposed on the sameaxis, an input shaft IS, an output shaft OS, eight shafts TM1 to TM8connected to at least one of rotation elements of the first, second,third, and fourth planetary gear sets PG1, PG2, PG3, and PG4, threeclutches C1 to C3 and three brakes B1 to B3 that are control elements,and a transmission housing H.

Torque input from the input shaft IS is changed by cooperation of thefirst, second, third, and fourth planetary gear sets PG1, PG2, PG3, andPG4, and the changed torque is output through the output shaft OS.

The planetary gear sets are disposed in a sequence of the first, second,third, and fourth planetary gear sets PG1, PG2, PG3, and PG4 from anengine.

The input shaft IS is an input member and the torque from a crankshaftof an engine, after being torque-converted through a torque converter,is input into the input shaft IS.

The output shaft OS is an output member, is disposed in parallel withthe input shaft IS, and transmits driving torque to a driving wheelthrough a differential apparatus.

The first planetary gear set PG1 is a double pinion planetary gear setand includes a first sun gear S1, a first ring gear R1 internallyengaged with a first pinion P1 externally engaged with the first sungear S1, and a first planet carrier PC1 rotatably supporting the firstpinion P1 respectively as first, second, and third rotation elements N1,N2, and N3.

The second planetary gear set PG2 is a single pinion planetary gear setand includes a second sun gear S2, a second planet carrier PC2 rotatablysupporting a second pinion P2 that is externally meshed with the secondsun gear S2, and a second ring gear R2 that is internally meshed withthe second pinion P2 respectively as fourth, fifth, and sixth rotationelements N4, N5, and N6.

The third planetary gear set PG3 is a single pinion planetary gear setand includes a third sun gear S3, a third planet carrier PC3 rotatablysupporting a third pinion P3 that is externally meshed with the thirdsun gear S3, and a third ring gear R3 that is internally meshed with thethird pinion P3 respectively as seventh, eighth, and ninth rotationelements N7, N8, and N9.

The fourth planetary gear set PG4 is a single pinion planetary gear setand includes a fourth sun gear S4, a fourth planet carrier PC4 rotatablysupporting a fourth pinion P4 that is externally meshed with the fourthsun gear S4, and a fourth ring gear R4 that is internally meshed withthe fourth pinion P4 respectively as tenth, eleventh, and twelfthrotation elements N10, N11, and N12.

The second rotation element N2 is directly connected with the sixthrotation element N6 and the ninth rotation element TM9, the fifthrotation element N5 is directly connected with the eleventh rotationelement N11, and the eighth rotation element N8 is directly connectedwith the tenth rotation element N10 such that the first, second, third,and fourth planetary gear sets PG1, PG2, PG3, and PG4 includes eightrotation shafts TM1 to TM8.

The eight shafts TM1 to TM8 will be described in further detail.

The first rotation shaft TM1 is directly connected to the first rotationelement N1 (first sun gear S1) and is directly connected to the inputshaft IS so as to be operated as an input element continuously.

The second rotation shaft TM2 directly connects the second rotationelement N2 (first ring gear R1) with the sixth rotation element N6(second ring gear R2) and the ninth rotation element N9 (third ring gearR3), and is selectively connected to the transmission housing H so as tobe operated as a selectively fixed element.

The third rotation shaft TM3 is directly connected to the third rotationelement N3 (first planet carrier PC1) and is selectively connected tothe transmission housing H so as to be operated as a selectively fixedelement.

The fourth rotation shaft TM4 is directly connected to the fourthrotation element N4 (second sun gear S2) and is selectively connected tothe transmission housing H so as to be operated as a selectively fixedelement.

The fifth rotation shaft TM5 directly connects the fifth rotationelement N5 (second planet carrier PC2) with the eleventh rotationelement N11 (fourth planet carrier PC4) and is selectively connected tothe input shaft IS so as to be operated as a selective input element.

The sixth rotation shaft TM6 is directly connected to the seventhrotation element N7 (third sun gear S3), is selectively connected to theinput shaft IS so as to be operated as a selective input element, and isselectively connected to the third rotation shaft TM3.

The seventh rotation shaft TM7 directly connects the eighth rotationelement N8 (third planet carrier PC3) with the tenth rotation elementN10 (fourth sun gear S4).

The eighth rotation shaft TM8 is directly connected to the twelfthrotation element N12 (fourth ring gear R4) and is directly connected tothe output shaft OS so as to be operated as an output elementcontinuously.

In addition, three clutches C1, C2, and C3 that are control elements aredisposed at positions at which two rotation shafts among the rotationshafts TM1 to TM8 are selectively connected to each other.

In addition, three brakes B1, B2, and B3 that are control elements aredisposed at positions at which any one rotation shaft among the rotationshafts TM1 to TM8 is selectively connected to the transmission housingH.

Arrangements of the six control elements C1 to C3 and B1 to B3 aredescribed in detail.

The first clutch C1 is disposed between the input shaft IS and the fifthrotation shaft TM5 and selectively connects the input shaft IS with thefifth rotation shaft TM5.

The second clutch C2 is disposed between the input shaft IS and thesixth rotation shaft TM6 and selectively connects the input shaft ISwith the sixth rotation shaft TM6.

The third clutch C3 is disposed between the third rotation shaft TM3 andthe sixth rotation shaft TM6 and selectively connects the third rotationshaft TM3 with the sixth rotation shaft TM6.

The first brake B1 is disposed between the second rotation shaft TM2 andthe transmission housing H and causes the second rotation shaft TM2 tobe operated as the selectively fixed element.

The second brake B2 is disposed between the third rotation shaft TM3 andthe transmission housing H and causes the third rotation shaft TM3 to beoperated as the selectively fixed element.

The third brake B3 is disposed between the fourth rotation shaft TM4 andthe transmission housing H and causes the fourth rotation shaft TM4 tobe operated as the selectively fixed element.

The control elements including the first, second, and third clutches C1,C2, and C3 and the first, second, and third brakes B1, B2, and B3 may bemulti-plates friction elements of wet type that are operated byhydraulic pressure.

FIG. 2 is an operation chart of control elements at each speed stage inthe planetary gear train according to various embodiments of the presentinvention.

As shown in FIG. 2, three control elements are operated at each speedstage in the planetary gear train according to various embodiments ofthe present invention.

The third clutch C3 and the first and third brakes B1 and B3 aresimultaneously operated at a first forward speed stage D1. In a statethat the third rotation shaft TM3 is connected to the sixth rotationshaft TM6 by operation of the third clutch C3, the torque of the inputshaft IS is input to the first rotation shaft TM1. In addition, thesecond and fourth rotation shafts TM2 and TM4 are operated as the fixedelements by operation of the first and third brakes B1 and B3.Therefore, the torque of the input shaft IS is shifted into the firstforward speed stage, and the first forward speed stage is output to theoutput shaft OS connected to the eighth rotation shaft TM8.

The third clutch C3 and the second and third brakes B2 and B3 aresimultaneously operated at a second forward speed stage D2. In a statethat the third rotation shaft TM3 is connected to the sixth rotationshaft TM6 by operation of the third clutch C3, the torque of the inputshaft IS is input to the first rotation shaft TM1. In addition, thethird and fourth rotation shafts TM3 and TM4 are operated as the fixedelements by operation of the second and third brakes B2 and B3.Therefore, the torque of the input shaft IS is shifted into the secondforward speed stage, and the second forward speed stage is output to theoutput shaft OS connected to the eighth rotation shaft TM8.

The second and third clutches C2 and C3 and the third brake B3 aresimultaneously operated at a third forward speed stage D3. In a statethat the input shaft IS is connected to the sixth rotation shaft TM6 byoperation of the second clutch C2 and the third rotation shaft TM3 isconnected to the sixth rotation shaft TM6 by operation of the thirdclutch C3, the torque of the input shaft IS is input to the firstrotation shaft TM1 and the sixth rotation shaft TM6. In addition, thefourth rotation shaft TM4 is operated as the fixed element by operationof the third brake B3. Therefore, the torque of the input shaft IS isshifted into the third forward speed stage, and the third forward speedstage is output to the output shaft OS connected to the eighth rotationshaft TM8.

The first and third clutches C1 and C3 and the third brake B3 aresimultaneously operated at a fourth forward speed stage D4. In a statethat the input shaft IS is connected to the fifth rotation shaft TM5 byoperation of the first clutch C1 and the third rotation shaft TM3 isconnected to the sixth rotation shaft TM6 by operation of the thirdclutch C3, the torque of the input shaft IS is input to the firstrotation shaft TM1 and the fifth rotation shaft TM5. In addition, thefourth rotation shaft TM4 is operated as the fixed element by operationof the third brake B3. Therefore, the torque of the input shaft IS isshifted into the fourth forward speed stage, and the fourth forwardspeed stage is output to the output shaft OS connected to the eighthrotation shaft TM8.

The first and second clutches C1 and C2 and the third brake B3 aresimultaneously operated at a fifth forward speed stage D5. In a statethat the input shaft IS is connected to the fifth rotation shaft TM5 byoperation of the first clutch C1 and is connected to the sixth rotationshaft TM6 by operation of the second clutch C2, the torque of the inputshaft IS is input to the first, fifth, and sixth rotation shafts TM1,TM5, and TM6. In addition, the fourth rotation shaft TM4 is operated asthe fixed element by operation of the third brake B3. Therefore, thetorque of the input shaft IS is shifted into the fifth forward speedstage, and the fifth forward speed stage is output to the output shaftOS connected to the eighth rotation shaft TM8.

The first, second, and third clutches C1, C2, and C3 are simultaneouslyoperated at a sixth forward speed stage D6. In a state that the inputshaft IS is connected to the fifth rotation shaft TM5 by operation ofthe first clutch C1 and is connected to the sixth rotation shaft TM6 byoperation of the second clutch C2 and the third rotation shaft TM3 isconnected to the sixth rotation shaft TM6 by operation of the thirdclutch C3, the torque of the input shaft IS is input to the first,fifth, and sixth rotation shafts TM1, TM5, and TM6. Therefore, all ofthe first, second, third, and fourth planetary gear sets PG1, PG2, PG3,and PG4 become lock-up state. Therefore, the torque of the input shaftIS is shifted into the sixth forward speed stage, and the sixth forwardspeed stage is output to the output shaft OS connected to the eighthrotation shaft TM8. The same rotational speed as the input shaft IS isoutput at the sixth forward speed stage.

The first and second clutches C1 and C2 and the second brake B2 aresimultaneously operated at a seventh forward speed stage D7. In a statethat the input shaft IS is connected to the fifth rotation shaft TM5 byoperation of the first clutch C1 and is connected to the sixth rotationshaft TM6 by operation of the second clutch C2, the torque of the inputshaft IS is input to the first, fifth, and sixth rotation shafts TM1,TM5, and TM6. In addition, the third rotation shaft TM3 is operated asthe fixed element by operation of the second brake B2. Therefore, thetorque of the input shaft IS is shifted into the seventh forward speedstage, and the seventh forward speed stage is output to the output shaftOS connected to the eighth rotation shaft TM8.

The first and third clutches C1 and C3 and the second brake B2 aresimultaneously operated at an eighth forward speed stage D8. In a statethat the input shaft IS is connected to the fifth rotation shaft TM5 byoperation of the first clutch C1 and the third rotation shaft TM3 isconnected to the sixth rotation shaft TM6 by operation of the thirdclutch C3, the torque of the input shaft IS is input to the firstrotation shaft TM1 and the fifth rotation shaft TM5. In addition, thethird rotation shaft TM3 is operated as the fixed element by operationof the second brake B2. Therefore, the torque of the input shaft IS isshifted to the eighth forward speed stage, and the eighth forward speedstage is output to the output shaft OS connected to the eighth rotationshaft TM8.

The first and third clutches C1 and C3 and the first brake B1 aresimultaneously operated at a ninth forward speed stage D9. In a statethat the input shaft IS is connected to the fifth rotation shaft TM5 byoperation of the first clutch C1 and the third rotation shaft TM3 isconnected to the sixth rotation shaft TM6 by operation of the thirdclutch C3, the torque of the input shaft IS is input to the firstrotation shaft TM1 and the fifth rotation shaft TM5. In addition, thesecond rotation shaft TM2 is operated as the fixed element by operationof the first brake B1. Therefore, the torque of the input shaft IS isshifted into the ninth forward speed stage, and the ninth forward speedstage is output to the output shaft OS connected to the eighth rotationshaft TM8.

The second clutch C2 and the first and third brakes B1 and B3 aresimultaneously operated at a reverse speed stage REV. In a state thatthe input shaft IS is connected to the sixth rotation shaft TM6, thetorque of the input shaft IS is input to the first rotation shaft TM1and the sixth rotation shaft TM6. In addition, the second and fourthrotation shafts TM2 and TM4 are operated as the fixed elements byoperation of the first and third brakes B1 and B3. Therefore, the torqueof the input shaft IS is shifted into the reverse speed stage, and thereverse speed stage is output to the output shaft OS connected to theeighth rotation shaft TM8.

The planetary gear train according to various embodiments of the presentinvention may achieve at least nine forward speed stages and one reversespeed stage by combining four planetary gear sets PG1, PG2, PG3, and PG4with the three clutches C1, C2, and C3 and the three brakes B1, B2, andB3.

In addition, since gear ratio span greater than 9.3 is secured, drivingefficiency of the engine may be maximized.

In addition, step ratios between neighboring speed stages except betweenthe seventh forward speed stage and the eighth forward speed stage areof magnitude 1.2 or more in the planetary gear train according tovarious embodiments of the present invention. In addition, sincelinearity of step ratios can be secured due to multiple speed stages,drivability such as acceleration before and after shift, rhythmicalengine speed, and the like may be improved.

The foregoing descriptions of specific exemplary embodiments of thepresent invention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteachings. The exemplary embodiments were chosen and described in orderto explain certain principles of the invention and their practicalapplication, to thereby enable others skilled in the art to make andutilize various exemplary embodiments of the present invention, as wellas various alternatives and modifications thereof. It is intended thatthe scope of the invention be defined by the Claims appended hereto andtheir equivalents.

What is claimed is:
 1. A planetary gear train of an automatictransmission for a vehicle comprising: an input shaft to receive torqueof an engine; an output shaft to output changed torque of the engine; afirst planetary gear set including a first rotation element, a secondrotation element, and a third rotation element; a second planetary gearset including a fourth rotation element, a fifth rotation element, and asixth rotation element; a third planetary gear set including a seventhrotation element, an eighth rotation element, and a ninth rotationelement; and a fourth planetary gear set including a tenth rotationelement, an eleventh rotation element, and a twelfth rotation element,wherein the input shaft is directly connected to the first rotationelement, the output shaft is directly connected to the twelfth rotationelement, the second rotation element is directly connected to the sixthrotation element and the ninth rotation element, the fifth rotationelement is directly connected to the eleventh rotation element, theeighth rotation element is directly connected to the tenth rotationelement, and the second rotation element is selectively connected to atransmission housing.
 2. The planetary gear train of claim 1, whereinthe third rotation element is selectively connected to the transmissionhousing, the fourth rotation element is selectively connected to thetransmission housing, the input shaft is selectively connected to theeleventh rotation element, the input shaft is selectively connected tothe seventh rotation element, and the third rotation element isselectively connected to the seventh rotation element.
 3. The planetarygear train of claim 1, wherein the first rotation element, the secondrotation element, and the third rotation element comprise a first sungear, a first ring gear, and a first planet carrier, the fourth rotationelement, the fifth rotation element, and the sixth rotation elementcomprise a second sun gear, a second planet carrier, and a second ringgear, the seventh rotation element, the eighth rotation element, and theninth rotation element comprise a third sun gear, a third planetcarrier, and a third ring gear, and the tenth rotation element, theeleventh rotation element, and the twelfth rotation element comprise afourth sun gear, a fourth planet carrier, and a fourth ring gear.
 4. Theplanetary gear train of claim 2, further comprising: a first clutchselectively connecting the input shaft to the eleventh rotation element;a second clutch selectively connecting the input shaft to the seventhrotation element; a third clutch selectively connecting the thirdrotation element to the seventh rotation element; a first brakeselectively connecting the second rotation element to the transmissionhousing; a second brake selectively connecting the third rotationelement to the transmission housing; and a third brake selectivelyconnecting the fourth rotation element to the transmission housing.
 5. Aplanetary gear train of an automatic transmission for a vehiclecomprising: an input shaft configured for receiving torque of an engine;an output shaft configured for outputting changed torque of the engine;a first planetary gear set including a first rotation element, a secondrotation element, and a third rotation element; a second planetary gearset including a fourth rotation element, a fifth rotation element, and asixth rotation element; a third planetary gear set including a seventhrotation element, an eighth rotation element, and a ninth rotationelement; a fourth planetary gear set including a tenth rotation element,an eleventh rotation element, and a twelfth rotation element; a firstrotation shaft directly connected to the first rotation element anddirectly connected to the input shaft; a second rotation shaft directlyconnecting the second rotation element to the sixth rotation element andthe ninth rotation element, and selectively connected to a transmissionhousing; a third rotation shaft directly connected to the third rotationelement and selectively connected to the transmission housing; a fourthrotation shaft directly connected to the fourth rotation element andselectively connected to the transmission housing; a fifth rotationshaft directly connecting the fifth rotation element to the eleventhrotation element and selectively connected to the input shaft; a sixthrotation shaft directly connected to the seventh rotation element andselectively connected to the input shaft or the third rotation shaft; aseventh rotation shaft directly connecting the eighth rotation elementto the tenth rotation element; and an eighth rotation shaft directlyconnected to the twelfth rotation element and directly connected to theoutput shaft.
 6. The planetary gear train of claim 5, wherein the firstplanetary gear set is a double pinion planetary gear set, the firstrotation element is a first sun gear, the second rotation element is afirst ring gear, and the third rotation element is a first planetcarrier, the second planetary gear set is a single pinion planetary gearset, the fourth rotation element is a second sun gear, the fifthrotation element is a second planet carrier, and the sixth rotationelement is a second ring gear, the third planetary gear set is a singlepinion planetary gear set, the seventh rotation element is a third sungear, the eighth rotation element is a third planet carrier, and theninth rotation element is a third ring gear, and the fourth planetarygear set is a single pinion planetary gear set, the tenth rotationelement is a fourth sun gear, the eleventh rotation element is a fourthplanet carrier, and the twelfth rotation element is a fourth ring gear.7. The planetary gear train of claim 5, further comprising: a firstclutch selectively connecting the input shaft to the fifth rotationshaft; a second clutch selectively connecting the input shaft to thesixth rotation shaft; a third clutch selectively connecting the thirdrotation shaft to the sixth rotation shaft; a first brake selectivelyconnecting the second rotation shaft to the transmission housing; asecond brake selectively connecting the third rotation shaft to thetransmission housing; and a third brake selectively connecting thefourth rotation shaft to the transmission housing.
 8. The planetary geartrain of claim 7, wherein a first forward speed stage is achieved byoperation of the third clutch and the first and third brakes, a secondforward speed stage is achieved by operation of the third clutch and thesecond and third brakes, a third forward speed stage is achieved byoperation of the second and third clutches and the third brake, a fourthforward speed stage is achieved by operation of the first and thirdclutches and the third brake, a fifth forward speed stage is achieved byoperation of the first clutch and the second clutch and the third brake,a sixth forward speed stage is achieved by operation of the first,second, and third clutches, a seventh forward speed stage is achieved byoperation of the first clutch and the second clutch and the secondbrake, an eighth forward speed stage is achieved by operation of thefirst and third clutches and the second brake, a ninth forward speedstage is achieved by operation of the first and third clutches and thefirst brake, and a reverse speed stage is achieved by operation of thesecond clutch and the first and third brakes.
 9. A planetary gear trainof an automatic transmission for a vehicle comprising: an input shaftconfigured for receiving torque of an engine; an output shaft configuredfor outputting changed torque of the engine; a first planetary gear setcomprising a double pinion planetary gear set including a first rotationelement, a second rotation element, and a third rotation element; asecond planetary gear set comprising a single pinion planetary gear setincluding a fourth rotation element, a fifth rotation element, and asixth rotation element; a third planetary gear set comprising a singlepinion planetary gear set including a seventh rotation element, aneighth rotation element, and a ninth rotation element; a fourthplanetary gear set comprising a single pinion planetary gear setincluding a tenth rotation element, an eleventh rotation element, and atwelfth rotation element; a first rotation shaft directly connected tothe first rotation element and directly connected to the input shaft; asecond rotation shaft directly connecting the second rotation element tothe sixth rotation element and the ninth rotation element, andselectively connected to a transmission housing; a third rotation shaftdirectly connected to the third rotation element and selectivelyconnected to the transmission housing; a fourth rotation shaft directlyconnected to the fourth rotation element and selectively connected tothe transmission housing; a fifth rotation shaft directly connecting thefifth rotation element to the eleventh rotation element and selectivelyconnected to the input shaft; a sixth rotation shaft directly connectedto the seventh rotation element and selectively connected to the inputshaft or the third rotation shaft; a seventh rotation shaft directlyconnecting the eighth rotation element to the tenth rotation element; aneighth rotation shaft directly connected to the twelfth rotation elementand directly connected to the output shaft; a first clutch selectivelyconnecting the input shaft to the fifth rotation shaft; a second clutchselectively connecting the input shaft to the sixth rotation shaft; athird clutch selectively connecting the third rotation shaft to thesixth rotation shaft; a first brake selectively connecting the secondrotation shaft to the transmission housing; a second brake selectivelyconnecting the third rotation shaft to the transmission housing; and athird brake selectively connecting the fourth rotation shaft to thetransmission housing.
 10. The planetary gear train of claim 9, whereinthe first rotation element, the second rotation element, and the thirdrotation element are a first sun gear, a first ring gear, and a firstplanet carrier, the fourth rotation element, the fifth rotation element,and the sixth rotation element are a second sun gear, a second planetcarrier, and a second ring gear, the seventh rotation element, theeighth rotation element, and the ninth rotation element are a third sungear, a third planet carrier, and a third ring gear, and the tenthrotation element, the eleventh rotation element, and the twelfthrotation element are a fourth sun gear, a fourth planet carrier, and afourth ring gear.
 11. The planetary gear train of claim 9, wherein afirst forward speed stage is achieved by operation of the third clutchand the first and third brakes, a second forward speed stage is achievedby operation of the third clutch and the second and third brakes, athird forward speed stage is achieved by operation of the second andthird clutches and the third brake, a fourth forward speed stage isachieved by operation of the first and third clutches and the thirdbrake, a fifth forward speed stage is achieved by operation of the firstclutch and the second clutch and the third brake, a sixth forward speedstage is achieved by operation of the first, second, and third clutches,a seventh forward speed stage is achieved by operation of the firstclutch and the second clutch and the second brake, an eighth forwardspeed stage is achieved by operation of the first and third clutches andthe second brake, a ninth forward speed stage is achieved by operationof the first and third clutches and the first brake, and a reverse speedstage is achieved by operation of the second clutch and the first andthird brakes.